diff --git a/include/aoc/DiskFragmenter.hpp b/include/aoc/DiskFragmenter.hpp
new file mode 100644
index 0000000..64d538f
--- /dev/null
+++ b/include/aoc/DiskFragmenter.hpp
@@ -0,0 +1,31 @@
+// Solutions to the Advent Of Code 2024.
+// Copyright (C) 2025  Stefan Müller
+//
+// This program is free software: you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free Software
+// Foundation, either version 3 of the License, or (at your option) any later
+// version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <aoc/Solver.hpp>
+
+class DiskFragmenter
+    : public Solver
+{
+public:
+    virtual const std::string getPuzzleName() const override;
+    virtual const std::string getInputFileName() const override;
+    virtual void processDataLine(const std::string& line) override;
+    virtual void finish() override;
+private:
+    int getDigit(const std::string& line, const size_t index) const;
+    long long int calcChecksumPart(const size_t idNumber, const int nBlocks, size_t& position) const;
+};
diff --git a/src/DiskFragmenter.cpp b/src/DiskFragmenter.cpp
new file mode 100644
index 0000000..793a326
--- /dev/null
+++ b/src/DiskFragmenter.cpp
@@ -0,0 +1,103 @@
+// Solutions to the Advent Of Code 2024.
+// Copyright (C) 2025  Stefan Müller
+//
+// This program is free software: you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free Software
+// Foundation, either version 3 of the License, or (at your option) any later
+// version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include <aoc/DiskFragmenter.hpp>
+
+const std::string DiskFragmenter::getPuzzleName() const
+{
+    return "Day 9: Disk Fragmenter";
+}
+
+const std::string DiskFragmenter::getInputFileName() const
+{
+    return "disk_fragmenter.txt";
+}
+
+void DiskFragmenter::processDataLine(const std::string& line)
+{
+    //size_t maxIdNumber{ line.size() / 2 };
+    // Index of the first unprocessed digit in the disk map.
+    size_t front{ 0 };
+    // ID number of the file 'front' refers to (when 'isFile == true'). Equivalent to 'front / 2', but calculated
+    // incrementally.
+    size_t frontIdNumber{ 0 };
+    // Index of the last unprocessed digit in the disk map.
+    size_t back{ line.size() - 1 };
+    // Number of remaining fragmented blocks in the file that 'back' refers to (when 'isFile == true').
+    int nRemainingBackBlocks{ getDigit(line, back) };
+    // ID number of the file 'back' refers to (when 'isFile == true'). Equivalent to 'back / 2', but calculated
+    // incrementally.
+    size_t backIdNumber{ line.size() / 2 };
+    // Current block position.
+    size_t position{ 0 };
+
+    bool isFile{ true };
+
+    while (front < back)
+    {
+        if (isFile)
+        {
+            // Adds the checksum for the file at 'front'.
+            int nFileBlocks = getDigit(line, front);
+            part1 += calcChecksumPart(frontIdNumber, nFileBlocks, position);
+            frontIdNumber++;
+        }
+        else
+        {
+            int nFreeBlocks = getDigit(line, front);
+            while (nFreeBlocks > 0)
+            {
+                if (nFreeBlocks >= nRemainingBackBlocks)
+                {
+                    // Adds the checksum for all the blocks of the file at 'back'.
+                    part1 += calcChecksumPart(backIdNumber, nRemainingBackBlocks, position);
+                    backIdNumber--;
+
+                    nFreeBlocks -= nRemainingBackBlocks;
+                    back -= 2;
+                    nRemainingBackBlocks = getDigit(line, back);
+                }
+                else
+                {
+                    // Adds the checksum for the blocks of the file at 'back' that fit into the empty blocks at 'front'.
+                    part1 += calcChecksumPart(backIdNumber, nFreeBlocks, position);
+
+                    nRemainingBackBlocks -= nFreeBlocks;
+                    nFreeBlocks = 0;
+                }
+            }
+        }
+        front++;
+        isFile = !isFile;
+    }
+
+    // Adds the checksum for the remaining blocks of the file at 'back'.
+    part1 += calcChecksumPart(backIdNumber, nRemainingBackBlocks, position);
+}
+
+void DiskFragmenter::finish()
+{
+}
+
+int DiskFragmenter::getDigit(const std::string& line, const size_t index) const
+{
+    return line[index] - '0';
+}
+
+long long int DiskFragmenter::calcChecksumPart(const size_t idNumber, const int nBlocks, size_t& position) const
+{
+    position += nBlocks;
+    return idNumber * ((nBlocks * (2 * position - nBlocks - 1)) / 2);
+}
diff --git a/src/Program.cpp b/src/Program.cpp
index a2358b0..8d3f1f1 100644
--- a/src/Program.cpp
+++ b/src/Program.cpp
@@ -29,6 +29,7 @@
 #include <aoc/GuardGallivant.hpp>
 #include <aoc/BridgeRepair.hpp>
 #include <aoc/ResonantCollinearity.hpp>
+#include <aoc/DiskFragmenter.hpp>
 #include <aoc/HoofIt.hpp>
 #include <aoc/PlutonianPebbles.hpp>
 #include <aoc/LanParty.hpp>
@@ -57,6 +58,7 @@ void Program::runSolvers()
     runSolver<GuardGallivant>(solverEngine);
     runSolver<BridgeRepair>(solverEngine);
     runSolver<ResonantCollinearity>(solverEngine);
+    runSolver<DiskFragmenter>(solverEngine);
     runSolver<HoofIt>(solverEngine);
     runSolver<PlutonianPebbles>(solverEngine);
     runSolver<LanParty>(solverEngine);
diff --git a/tests/src/TestCases.cpp b/tests/src/TestCases.cpp
index cb592a4..e0a875c 100644
--- a/tests/src/TestCases.cpp
+++ b/tests/src/TestCases.cpp
@@ -135,6 +135,19 @@ TEST_CASE("[ResonantCollinearityTests]")
     }
 }
 
+TEST_CASE("[DiskFragmenterTests]")
+{
+    TestContext test;
+    SECTION("FullData")
+    {
+        test.run(std::make_unique<DiskFragmenter>(), 6401092019345, 0, test.getInputPaths());
+    }
+    SECTION("ExampleData")
+    {
+        test.run(std::make_unique<DiskFragmenter>(), 1928, 0, test.getExampleInputPaths());
+    }
+}
+
 TEST_CASE("[HoofItTests]")
 {
     TestContext test;